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Author Topic: Cable raceway/tray/trough in stage wings flush with floor - code compliant?  (Read 1535 times)

Ethan Montgomery

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I've spent a couple hours researching this forum and elsewhere, and can't seem to find an answer, so here goes.

Here's the scenario - let's imagine a typical 'theater' type stage with wings on stage left and right.  At the outside edges of the wings are walls where there are installed power outlets, which will supply power to a bunch of stringers on stage.  Necessarily, this means a bunch of cables laying across the floor of the wing, creating a trip hazard (and impeding rolling cases, etc).

Can a (relatively shallow) trough be installed into the floor between the wall and the edge of the stage (along the floor of the wing), with perhaps a folding cover, to run the power cables from the wall to the stage?  Think effectively a Yellow Jacket/cable ramp that is made to be flush with the surrounding floor.

I've found a bunch of info regarding conduit and raceway as it pertains to permanent installs (not that I totally understand all of it), but this wouldn't be exactly that per se.  To provide a more specifics - let's say it's a bunch of L5-20 permanently installed outlets along the wall at the outside perimeter of the stage wing.  From there, SOOW cables will plug into the wall outlets, then run to various stringers around the stage (which obviously move from show-to-show, I believe making this a 'portable' application?).  The idea is to get these "under" the floor in the wings so that everything is flush, and doesn't impede either foot traffic or rolling equipment.

One hypothetical plan - to make it even more specific - would be to raise the floor in the wings some height (maybe ~6-12"?) above the level of the stage itself.  Then a long thin portion of the raised floor can flip up - just like a yellow jacket/cable ramp - revealing the trough below.  Obviously the lid would need some structural integrity to support weight on top of it, but I don't think that's relevant here.  The wall end and stage end will necessarily be 'wide open' in some fashion (perhaps a hole with the same cross section as the trough, but facing up toward the wall at that end, and facing parallel to the stage at the other end, exiting the raised floor at stage level?).  I.e., the wing's floor is level with the lid of the trough, and the stage is level with the bottom of the trough.  This would probably require some sort of ramp(s) down from the wing level to stage level for people and equipment, but I don't think that's relevant here.

What NEC/NFPA guideline(s) might cover this?  Or is this a total non-issue and I'm overthinking it?  Despite this scenario being a 'permanent' venue, I believe that because the cables are terminated with stringers that can move around the stage, this is strictly a 'portable' scenario.  I.e., rules governing the use of conduit and THHN/NM wiring for hardwired stage pockets, etc has little-to-nothing to do with this scenario.  This is SOOW cable terminating in movable stringers all sitting atop the stage.  Really I just want to cover the cables in the wings to keep people/equipment/cables safe from trip hazards and damage, and keep it all flush with the floor in the wing.

For even *further* elaboration - the concept would be expanded to xlr subsnakes and speaker wire for the stage as well - but I should think that at most, the same rules would apply, with perhaps at most separate troughs for each (either by requirement or just best practices).

Any thoughts or info is appreciated - thanks!
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Scott Hofmann

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One hypothetical plan - to make it even more specific - would be to raise the floor in the wings some height (maybe ~6-12"?) above the level of the stage itself.  Then a long thin portion of the raised floor can flip up - just like a yellow jacket/cable ramp - revealing the trough below.  Obviously the lid would need some structural integrity to support weight on top of it, but I don't think that's relevant here.  The wall end and stage end will necessarily be 'wide open' in some fashion (perhaps a hole with the same cross section as the trough, but facing up toward the wall at that end, and facing parallel to the stage at the other end, exiting the raised floor at stage level?).  I.e., the wing's floor is level with the lid of the trough, and the stage is level with the bottom of the trough.  This would probably require some sort of ramp(s) down from the wing level to stage level for people and equipment, but I don't think that's relevant here.

Hypothetically, you have destroyed all usefulness of your wing space by elevating it above stage level, even if a fraction of an inch instead of your six to twelve inches.
If it is indeed a “theater” type stage (your quotation marks), how would one move scenic units with caster clearance of less than an inch into the wings efficiently over any kind of ramp? Far different than road cases and on dark stages people would have trouble navigating any ramped area.
What happens at the offstage wall where there are usually doors or openings into adjoining spaces and you would have a huge transition to make?

Your idea is not without merit but you need to explore the exact construction of your stage floor. Many stage floors are layers of hardwood or plywood supported by a grid of “sleepers” (2x4’s laid flat) fastened to the concrete underneath. The point being there is actually a void of maybe 2 1/4” minimum from the underside of the top layer of the floor to the surface of the concrete. There is your chase or trough space already built in. The trick will be to cut out the trough lid and fit a replacement and its fasteners/hinges so as to to prevent trip hazards and remove any intersecting sleepers in the process. Whether this is code-compliant is another question.
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Scott Hofmann

Brian Adams

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I agree with Scott, raising the floor level of the wings is a terrible idea, unless you also raise the stage and give careful consideration to all other areas that it connects to. ADA specs for ramps are a minimum of 36" width and at least 12" of run for every 1" of rise. That means if you raised the wings 6" above stage height, your ramps would have to be at least 6' long. In my experience, you really don't want a ramp steeper than this, even if it doesn't need to be ADA compliant. I can't imagine anyone actually doing this to a stage. The construction would be a nightmare and the end result would be awkward.

I don't know all the details about running cable in troughs, but I'm vaguely aware of a type TC (tray cable) that's intended to be installed in those sorts of things, although not typically in an accessible area. I'm not sure if you'd be allowed to run SOOW though a trough, and if you did, you might not want to leave it for any longer than one show. If you can run SOOW down it, it's likely that you can run other stuff alongside it.

If I were doing this, I'd probably make the trough lids out of fairly thick aluminum or steel, in 3-5' lengths, with notches for cable exit every foot or two. 3/4" plywood might work, depending on the width and weight you need it to handle. You'd want them to be exactly even with the surrounding surface, with very little gap. It would be nice if they didn't slide around, and had either locating pins or hidden/flush hinges (not exposed hinges that protrude). Build them heavy, because they'll take a lot of abuse. I think they'll be really difficult to get right, so pay attention to the details. And no matter how you do it they'll probably be a little noisy when rolling things across. That might be a dealbreaker for theatre stuff, but maybe not. And they probably won't ever be in the perfect spot, but they might be close most of the time.

Why not just do floor pockets like everyone else? They're never in quite the right spot either, but they're usually close enough. And obviously they can meet code.

Also, I'm not an expert, so take all this with a grain of salt. Hopefully someone with in-depth knowledge of the code will chime in.
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Brian Adams
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Ethan Montgomery

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Hypothetically, you have destroyed all usefulness of your wing space by elevating it above stage level, even if a fraction of an inch instead of your six to twelve inches.
If it is indeed a “theater” type stage (your quotation marks), how would one move scenic units with caster clearance of less than an inch into the wings efficiently over any kind of ramp? Far different than road cases and on dark stages people would have trouble navigating any ramped area.
What happens at the offstage wall where there are usually doors or openings into adjoining spaces and you would have a huge transition to make?

Your idea is not without merit but you need to explore the exact construction of your stage floor. Many stage floors are layers of hardwood or plywood supported by a grid of “sleepers” (2x4’s laid flat) fastened to the concrete underneath. The point being there is actually a void of maybe 2 1/4” minimum from the underside of the top layer of the floor to the surface of the concrete. There is your chase or trough space already built in. The trick will be to cut out the trough lid and fit a replacement and its fasteners/hinges so as to to prevent trip hazards and remove any intersecting sleepers in the process. Whether this is code-compliant is another question.


I guess I should clarify that:

A) The idea is for a strictly music venue

B) It would not be using an existing structure.

I suppose it was a mistake for me to suggest that it's 'theater' style... I really just meant that it was a stage with wings.  I.e., space on the sides of the stage for amp racks, splitter, monitor consoles, etc.

Also, the notion of having a different level isn't integral at all to the idea... it was one thought about how the concept could be implemented (and I don't think would have the impact on the space's use for music the way it would, for example, for set pieces being moved around in the middle of a play - though point taken).

How about I put it this way:

From the side of the stage, let's say monitor world, or perhaps wherever the PD is located, you have a bunch of cabling running onto the stage.  To protect the cables from feet and casters as people and equipment get on and off the stage, you put it in a cable ramp.  This would be pretty standard practice in say, a temporary outdoor stage for a festival.

Now let's say instead of a temporary outdoor stage, it's a 'permanent' indoor music venue.  Can I effectively do the same thing, but just cut a channel in the floor such that the cable ramp sits flush with the surrounding floor?  It's still going to be (in the case of power), SOOW cable terminated in say, quad boxes that can be moved around the stage.

On one hand, my intuition would be to say of course that's not an issue, it's the exact same thing - with the bonus of being less of a trip hazard.  But I know that despite being "portable" (assuming I'm understanding that concept correctly) in that it's a bunch of quad boxes at the end of SOOW cable (and not floor pockets installed into the stage), it could also be considered "permanent" - which I think may change things.  Perhaps now the cable ramp is a 'conduit' or 'raceway', and I have to use THHN instead of SOOW?  This is precisely where my already very fuzzy understanding becomes exponentially fuzzier.

The problem basically is this:  There's a bunch of cabling at the side of the stage coming from the wall, monitor world, etc, that would be under-foot and under-caster along its path to the stage.  I want to protect it the same way that is typically done with cable ramps in 'temporary' settings.  The point of this exercise is to *not* use floor pockets.  Bonus points for making it flush with the floor.  Can this be done without violating some sort of NEC and/or NFPA code?  Is there any reason that a simple channel cut into the floor of sufficient depth - perhaps even just covered with a flush metal grate - would be treated any differently than if it were just sitting on the floor?
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Kevin Maxwell

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How about hanging it over the wing? Go up over and down. Basically install a flying tray in a few places have it be able to be dropped out of the tray where you need it to be. I would assume it would be behind the side stage teaser curtains. That is how we get cabling to some parts of the stage where we could never put something on the floor, for many reasons. It could even be motorized. 
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Stephen Swaffer

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One thing to keep in mind is that a major consideration with code specs other than physical protection is heat dissipation.  There are a number of tables in the NEC dealing with this-so a couple of cables in a trough is probably fine.  Even as few as 5-6 cables can be 10 to 24 current carrying conductors depending on the configuration which could result in a pretty serious derate of the cables.

Not a deal breaker but something to be aware of.
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Steve Swaffer

Doug Johnson

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I don't know if it would meet code for temporary service but Wiremold makes a surface flush floor duct called Trench Duct and they offer a removable cover for it.   I see the point of what you are trying to accomplish but, I think you maybe looking at the wrong solution.  A theater sized venue is typically going to have an installed sound system and power distribution should be included as part of that.  The types of acts that play these size rooms typically aren't going to be traveling with production and it will be cost prohibited to bring in outside production for every show if this is going to be full time venue.
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Eric Snodgrass

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If you end up with some kind of trough system you will end up with holes in the flooring where the cables must come out.  That ends up being a trip hazard anyway.  A hole in the stage is much more dangerous than a couple of power cables run along the floor.  And the trough system will probably match the color of the stage, thus making it harder to see in the typical lighting conditions of active stages. 
Still the best option is to use cables ramps that people can see and will know what they are, while routing cables cleanly and uniformly around the stage to minimize tripping hazards and leave large exit aisle open for the stage and equipment.  Usually that means running all power on the downstage edge for any gear downstage and running all the remaining power from the upstage area for any gear upstage. 
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Russell Ault

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I can't speak to the code issues (the CEC is quite different from the NEC when it comes to theatrical applications), but cable troughs are a feature at many of the smaller and mid-sized theatres in my area. Typically they ring the perimeter of the the stage (just offstage of the wings to just upstage of the cyc). They're typically ~30-45 cm wide, only ~5-10 cm deep, and are lidded with either ~3 mm steel on flush hinges or 3/4" plywood. Openings for cables are either a series of small notches on the non-hinged side of the metal lid (small enough to not be tripping hazards or catch casters), removable plugs between panels (these can be a tripping hazard if the plug is removed), or even just small gaps left between panels where a cable needs to come out (which might be a tripping hazard depending on the width of the gap). Some will even have power outlets available directly in the trough (although around here these are typically dimmed LX circuits).

The troughs are only for portable cable (any outlets installed in the trough will be wired from outside the trough or will use conduit), so the practice here is that line-voltage and low-voltage in the same trough shouldn't matter from a safety standpoint (any more than it does bundling a power cable with a mult, anyway). On the show I was working before all this started we had a few audio power runs, several dimmed LX runs, several mults, a couple loose audio channels, a network line, a couple fibre lines, a few baseband video feeds, etc. all tucked together into the (pretty full) stage right trough.

I can't speak to NEC code, but what your describing is common practice in my part of the world and does a good job keeping cables (and actors) safe.

-Russ
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Zach Greenhorn

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I can't speak to the code issues (the CEC is quite different from the NEC when it comes to theatrical applications), but cable troughs are a feature at many of the smaller and mid-sized theatres in my area. Typically they ring the perimeter of the the stage (just offstage of the wings to just upstage of the cyc). They're typically ~30-45 cm wide, only ~5-10 cm deep, and are lidded with either ~3 mm steel on flush hinges or 3/4" plywood. Openings for cables are either a series of small notches on the non-hinged side of the metal lid (small enough to not be tripping hazards or catch casters), removable plugs between panels (these can be a tripping hazard if the plug is removed), or even just small gaps left between panels where a cable needs to come out (which might be a tripping hazard depending on the width of the gap). Some will even have power outlets available directly in the trough (although around here these are typically dimmed LX circuits).

The larger theatre I'm occasionally working calls at has a very similar trough setup. There's a ring around the stage, then through the back hallway and a room backstage out to the parking for video and audio trucks.  I don't believe we have any circuits in the troughs, there's separate stage pockets with the dimmed circuits.

I'm also in Western Canada, it is more common in this area for some reason?
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